The present invention relates to a rotary actuator, in particular for adjustable articles of furniture, including beds or mattress supports, for incorporation in a structure for adjustment of an element in it, e.g. adjustment of a backrest section and/or legrest section in a bed or mattress support.
On beds, no matter whether they are hospital beds or care beds or mattress supports for domestic use having an adjustable head end and typically also an adjustable foot end, it is common that the adjustment is carried out by means of linear actuators. An example of a hospital bed is found in EP 498 111 to J. Nesbit Evans (the name has been changed to Huntleigh Technology Plc), and an example of an actuator is found in EP 577 541 to Linak A/S. A special embodiment for separate mattress supports is seen in DE 38 42 078 to Niko (the name has been changed to OKIN). The actuators require much space, which is a drawback particularly in beds and mattress supports for domestic use. It applies to hospital beds that these have to be washed from time to time, which takes place at a temperature of 65xc2x0 C. in washing machines intended for the purpose. This makes special demands on the electrical adjustment mechanisms and the associated control equipment. These must inter alia be water-tight.
WO 99/40820 to Recticel discloses another example of an adjustment mechanism in which a tube shaft is rotated by means of a motor arranged at the end thereof. The structure has not been realized because of problems with the drive unit.
WO 92/20548 to Linvent AB discloses a drive of the above-mentioned type. This drive, which is based on a planetary gear structure, is particularly intended for front seats in cars, said drive serving as a mounting bracket for the backrest at one side and to adjust the inclination of the backrest.
In summary, the requirements to be met by adjustment mechanisms for beds are that they must have a relatively great strength, and that at the same time hey must be compact and comparatively noiseless as well as easy to mount. In addition, they must be capable of being constructed as a low volt structure. Further, the price must below.
The object of the invention is to provide a rotary actuator of the type mentioned in the opening paragraph which is capable of satisfying these different requirements. Also, it must be possible to manufacture the actuator at production costs which at least do not give a considerably higher price than the operationally reliable and well-tested linear actuators.
This is achieved according to the invention by a rotary actuator as defined in claim 1. It is hereby possible to use the same motor type as in linear actuators, i.e. a low volt motor having a relatively high number of revolutions which is reduced in the subsequent transmission. The planetary gear itself can be made relatively small and yet be able to transfer great forces, as the two outer rings distribute the forces more evenly in the gear and also support the planet wheels and the intermediate ring.
By providing the planetary gear with the number of teeth stated in claims 2-7 a high transmission reduction is achieved, and also a good transfer of forces may be achieved by shaping the planet wheels such that over their entire length they engage the toothed rims. It also simplifies the manufacture when the planet wheels have the same cross-section over the entire length. With the concretely stated number of teeth, a transmission of 1:53.2 is achieved. The central arrangement of the sun wheel has a stabilizing effect and also contributes to a good distribution of forces.
The two outer rings may be connected in various ways, e.g. with a combination of bolts and spacers, fishplates or integration in a tube member. Expediently, however, they are provided in or as a common housing which may readily be designed such that the mounting bracket may be secured on the end thereof. This gives an evident possibility of constructing the actuator such that it may be mounted at the end of a tube.
The actuator will readily be able to transfer the occurring forces if the planetary gear is made of machine steel and is tempered, but the manufacturing costs will be so high that the price per se will be an obstacle to the use of the actuator in furniture structures.
When, according to the invention, the planetary gear is made of sintered metal, a more reasonable production price may be achieved. The two outer rings may be made as two parts, each having a width, calculated in the longitudinal direction of the toothed rims, which is attractive for sintered metal manufacture, there being an upper limit to the height of the parts during pressing.
The two outer rings may be made as two halves which are assembled to a unit. Alternatively, two identical outer parts with an intermediate spacer, which also provides the opening for the mounting bracket of the intermediate ring. When the faces of the parts directed toward each other are formed with a pattern of male/female parts, these are secured against mutual rotation when they are clamped together. The splitting also makes it easier to manufacture the parts of sintered metal.
When, according to the invention, the parts with the two outer rings are made of plastics and the toothed rims themselves as an insert of sintered metal, a further reduction in the manufacturing costs may be achieved. It is hereby possible to make a single part of plastics with recesses for the toothed rims. To retain the toothed rims in the plastics part, the connection is provided as a splined connection so that the toothed rims may be inserted from the ends.
When, according to the invention, the ends of the toothed rims facing each other and the intermediate ring are formed with cooperating stepped arrangements, a good mutual control of these is achieved. The stepped arrangements are expediently made as a single step in that the toothed rims have an internal step at one end and an external step at the opposite end. The part will hereby have the same height throughout, which is advantageous for sintering.
In an embodiment, the planet wheels are made of sintered metal and carried by a steel shaft. In that case, however, it has been found advantageous to provide the planet wheels with a bearing bushing. The planet wheels are relatively long and border on what is possible with sintered metal. A better accuracy is achieved by making the planet wheels as two halves and assembling these on the shaft.
In an embodiment of the actuator according to the invention, the mounting brackets of the two outer rings and the intermediate ring are formed as arms for connection with the movable part and the stationary part, respectively, of the structure in which they are to be incorporated. Expediently, the arm of the outer rings is formed by plate material, mounted on a free end of one of the two outer rings. The arm of the intermediate ring is likewise expediently formed by a plate, the actual toothed rim being formed as an insert inserted into a recess in the plate material. In terms of costs, this is less expensive than making the intermediate ring and the arm as an integrated unit of sintered metal. A special structure consists of two relatively thin plates with flared edges and hole rim and assembled with the plane sides against each other. The flared hole rim simultaneously serves as a good guide for the insert of sintered metal. In the pressing, the flared hole rim may be formed with a spline for the fixing of the insert, which is formed with a corresponding spline. If the conditions of load permit; the arm may also be made of plastics, optionally with a single embedded metal plate as a support. For reasons of strength, however, it has been found expedient to make the arm of a stack of punched metal plates, preferably three. Another option is to make the arm of a thick laser-cut plate.
It will be appreciated that the actuator may be constructed such that the outer rings are fixed in the structure in which the actuator is to be incorporated, while the intermediate ring drives the movable element in the structure. The actuator may also be constructed conversely, so that the intermediate ring is fixed, while the outer rings drive the movable element.
According to the invention, the actuator is driven by an electric motor. This is typically a low volt motor according to the power current regulation, i.e. below 42.4 volts. A step-down transmission is typically interposed between the motor and the furniture drive, as the motor usually has a high number of revolutions. The motor and the transmission are expediently secured to a free end of one of the two outer rings, preferably so that the motor, the transmission and the outer rings are arranged on a common axis. This structure makes the actuator suitable for mounting at the end of a tube, e.g. so that the outer rings and the intermediate ring are disposed externally of the tube end, while the transmission and the motor are disposed inside the tube. However, the actuator may also be constructed such that also the outer rings and the intermediate ring are disposed completely inside the tube. The mounting bracket of the intermediate ring is then constructed as a carrier in engagement with the tube. This, internal arrangement provides a good possibility of achieving a moisture- or water-tight structure.
When, according to the invention, the motor is provided with radially protruding legs of an elastic material, preferably in the form of a belt with protruding legs which are pushed inwardly over the motor, said leas being intended for cooperation with the inner side of the tube into which the motor is inserted, a simple and vibration-damping support of the motor is achieved.
The subclaims define additional expedient structures of the actuator, and the advantages of these will appear from the description of the embodiment of the invention.